1. Field of the Invention
The present invention relates to a structure of an AC surface discharge type color plasma display panel of matrix display and a plasma display device comprising the plasma display panel (hereinafter referred to as xe2x80x9cPDPxe2x80x9d).
2. Description of the Background Art
FIG. 13 is a perspective view showing a cell structure of an AC surface discharge type PDP. FIG. 14 is a schematic view showing an arrangement of a scan electrode 102, a sustain electrode 103 and barrier ribs 108 viewed from the X direction shown in FIG. 13. In general, an AC surface discharge type PDP of matrix display consists of a front panel on the side of display surface and a rear panel opposed to the front panel with a discharge space interposed therebetween. On a main surface of a glass substrate 101 in the front panel (a surface on the side opposed to the rear panel), a plurality of pairs of scan electrodes 102 and sustain electrodes 103 (only a pair is shown in FIGS. 13 and 14) are each arranged parallelly and symmetrically with a discharge gap which is a core of discharge in each discharge cell interposed therebetween with a spacing of pixel pitch in the Z direction of these figures.
Referring to FIG. 14, the scan electrode 102 is constituted of a bus electrode 102a which extends in the Y direction of the figure and transparent electrodes 102b (102bR1, 102bG, 102bB and 102bR2 in FIG. 14) which are connected to the bus electrode 102a and protrude in the Z direction of the figure. Further, the sustain electrode 103 is constituted of a bus electrode 103a which extends in the Y direction and transparent electrodes 103b (103bR1, 103bG, 103bB and 103bR2 in FIG. 14) which are connected to the bus electrode 103a and protrude in the Z direction to define the discharge gaps between themselves and the transparent electrodes 102b. The lengths of the transparent electrodes 102b and 103b (L102b0 and L103b0) in the Z direction are equal and the widths thereof (WR0, WG0 and WB0) in the Y direction are equal among all the discharge cells. Further, the spacings (G0) of the discharge gaps in the Z direction are equal among all the discharge cells.
The transparent electrodes 102b and 103b are made of materials having a relatively high transmissivity of visible rays, such as ITO (Indium Tin Oxide) or SnO2 (NESA), and formed by thin film processing such as evaporation or CVD in many cases. Further, the bus electrodes 102a and 103a are made of materials having relatively low resistance, such as silver, aluminum, copper or multilayer film of chromium and copper, and formed by thick film processing using printing process or thin film processing using photosensitive paste.
Furthermore, on the main surface of the glass substrate 101, a dielectric layer 104 is formed covering the scan electrode 102 and the sustain electrode 103. A surface of the dielectric layer 104 (exposed to the discharge space) is covered with a protection film 105 made of MgO and the like having relatively high secondary emission ratio and excellent sputtering resistance against ions, electrons and the like generated from the discharge.
On a main surface of a glass substrate 106 in the rear panel (a surface on the side opposed to the front panel), a plurality of barrier ribs 108 having a predetermined height are formed extending in the Z direction between adjacent discharge cells in the Y direction, to define a discharge space between the front panel and the rear panel. Further, on the main surface of the glass substrate 106, a plurality of write electrodes 107 (107R, 107G and 107B in FIG. 13) are formed extending in the Z direction between the adjacent barrier ribs 108.
On a surface of a concave portion made by side surfaces of the barrier ribs 108 and the main surface of the glass substrate 106, predetermined phosphors 109 (109R, 109G and 109B in FIG. 13) corresponding to red (R), green (G) and blue (B), respectively, are coated, to cover the write electrodes 107. Further, in some times, an insulating layer is provided between the write electrode 107 and the phosphor 109.
The front panel and the rear panel are sealed to each other by a sealing member (not shown) provided on rims of the panels, bringing tops of the barrier ribs 108 and the protection film 105 into contact with each other. The discharge space of the PDP formed by the front panel, the rear panel and the sealing member and defined by the barrier ribs 108 is filled with a noble gas such as xenon which generates ultraviolet ray from a discharge and a dischargeable gas such as nitrogen or oxygen. The phosphors 109 are excited by the ultraviolet ray generated from the discharge to cause luminescence in respective colors.
FIG. 15 is a schematic view briefly illustrating a process for luminescence of the discharge cell in the background-art PDP. In the discharge cell to be lighted, a predetermined voltage is applied between the scan electrode 102 and the write electrode 107 to cause a discharge between these electrodes. This is termed writing discharge, and positive ions and electrons ionized by the writing discharge are accumulated as wall charges on surfaces of the phosphors 109 and the protection film 105.
In the discharge cell in which the wall charges are accumulated, when a voltage is applied to the sustain electrode 103, a creepage discharge starts through the discharge gap between the scan electrode 102 and the sustain electrode 103. After that, an alternating electric field is further produced in the scan electrode 102 and the sustain electrode 103, and a discharge is thereby repeatedly caused in the scan electrode 102 and the sustain electrode 103. This discharge, repeatedly occurring in the scan electrode 102 and the sustain electrode 103, is termed sustain discharge, and the ultraviolet rays generated from the sustain discharge excites the phosphors 109 and becomes visible rays to be radiated outside through the front panel.
In order to make a tone display in the PDP, generally adopted is the time division toning system in which the number of sustain discharges in one field period of an image is controlled to control the luminance. One field period is divided into some small time units called subfields (SF), and pulse voltages to cause the sustain discharge, the number of which is weighted on the binary basis, are inserted in each subfield. For example, when one field is divided into eight subfields (SF0 to SF7) and sustain pulses are inserted in the respective subfields at a ratio of 1:2:4:8:16:32:64:128, combination of any subfields allows representation of 256-level luminance. Such a control is made on the discharge cells for all the colors, to represent about 16,700,000 colors.
If white is displayed by using the PDP which adopts this time division toning system, when gains of respective input signals of red, green and blue are mixed at a ratio of 1:1:1, 256-level white can be displayed. When all the colors are displayed by the maximum gains, in particular, white of maximum luminance can be displayed theoretically. Herein, white refers to a color whose normal state is at a point of color temperature of 6500 K in the Planckian locus of CIE xy chromaticity diagram.
When white is actually displayed in the PDP, however, even if the phosphors 109R, 109G and 109B are irradiated with the same amount of ultraviolet rays at a mixture ratio of 1:1:1, white can not be displayed or the color temperature is lowered in some cases. These phenomena are caused by bad balance of obtained visible lights of colors or affected by the visible lights of discharge gas itself other than the those from the phosphors 109. Particularly, low color temperature is largely affected by luminescence characteristics of the blue phosphor 109B. For this reason, when white is displayed in the PDP, the gains of the input signals are controlled, with the gains for red and green made lower than that for blue. For example, the gains for red, green and blue are controlled as R:G:B=0.8:0.5:1, to display white of desired color temperature.
With the above control of input gains, however, 256-level tone display can not be achieved on red or green. In the PDP displaying 256-level tone for each color (16,700,000 colors), for example, when the respective input gains for the colors are controlled as R:G:B=0.8:0.5:1, the respective tones for red and green are lowered to 256xc3x970.8=204-level tone and 256xc3x970.5=128-level tone, relative to 256-level tone for blue, and the quality of tone display is markedly deteriorated.
An invention intended to set the color temperature of white to a proper value without controlling the input gains, in which the luminescence areas of the phosphors are varied depending on colors by varying the widths of the phosphors, is disclosed in Japanese Patent Application Laid-Open No. 10-308179 (1998). In the invention shown in the gazette, however, varying the widths of the phosphors causes variation in voltage margin of the discharge cells, leading to wrong discharge.
The present invention is directed to a plasma display panel. According to a first aspect of the present invention, the plasma display panel comprises: a first substrate serving as a display surface; a second substrate opposed to the first substrate with a discharge space interposed therebetween, the discharge space consisting of a plurality of unit discharge regions arranged in matrix; a first electrode and a second electrode formed on a main surface of the first substrate on the side of the discharge space, being paired with each other and provided for each row of the plurality of unit discharge regions; a third electrode formed on a main surface of the second substrate on the side of discharge space, being provided for each column of the plurality of unit discharge regions; and phosphors of two kinds or more formed on the main surface of the second substrate covering the third electrode, having different luminescent colors, and in the plasma display panel of the first aspect, the first electrode has a trunk portion extending in a first direction which is a direction of the row; and branch portions connected to the trunk portion, being provided for the plurality of unit discharge regions, respectively, and protruding in a second direction which is a direction of the column, the second electrode has a trunk portion extending in the first direction; and branch portions connected to the trunk portion of the second electrode, being provided for the plurality of unit discharge regions, respectively, and protruding in the second direction to define discharge gaps between the branch portions of the first and second electrodes, respectively, and the areas of the branch portions of at least one of the first electrode and the second electrode vary among the plurality of unit discharge regions, depending on the luminescent colors.
According to a second aspect of the present invention, in the plasma display panel of the first aspect, the widths of the branch portions of at least one of the first electrode and the second electrode in the first direction vary among the plurality of unit discharge regions, depending on the luminescent colors.
According to a third aspect of the present invention, in the plasma display panel of the first or second aspect, the lengths of the branch portions of at least one of the first electrode and the second electrode in the second direction vary among the plurality of unit discharge regions, depending on the luminescent colors.
According to a fourth aspect of the present invention, in the plasma display panel of the third aspect, the lengths of the branch portions of the first electrode in the second direction vary among the plurality of unit discharge regions, and the trunk portion of the first electrode is arranged on an end portion of one of the branch portions which has the shortest length in the second direction on the side opposite to corresponding one of the discharge gaps.
According to a fifth aspect of the present invention, in the plasma display panel of any one of the first to fourth aspects, the spacings of the discharge gaps in the second direction vary among the plurality of unit discharge regions, depending on the luminescent colors.
According to a sixth aspect of the present invention, in the plasma display panel of any one of the first to fifth aspects, the areas of the branch portions of either one of the first electrode and the second electrode vary among the plurality of unit discharge regions.
According to a seventh aspect of the present invention, in the plasma display panel of the sixth aspect, the trunk portion of the first electrode and the branch portions of the first electrode are formed of the same material as a unit.
According to an eighth aspect of the present invention, in the plasma display panel of any one of the first to seventh aspects, the branch portions of the first electrode are frame-like metal electrodes having the same shape as rims of the branch portions.
According to a ninth aspect of the present invention, in the plasma display panel of the eighth aspect, the trunk portion of the first electrode is a metal electrode, and the trunk portion of the first electrode and the branch portions of the first electrode are formed as a unit.
According to a tenth aspect of the present invention, in the plasma display panel of the ninth aspect, the trunk portion of the first electrode is formed only outside the rims of the branch portions of the first electrode.
According to an eleventh aspect of the present invention, the plasma display panel comprises: a first substrate serving as a display surface; a second substrate opposed to the first substrate with a discharge space interposed therebetween, the discharge space consisting of a plurality of unit discharge regions arranged in matrix; a first electrode and a second electrode formed on a main surface of the first substrate on the side of the discharge space, being paired with each other and provided for each row of the plurality of unit discharge regions; a third electrode formed on a main surface of the second substrate on the side of discharge space, being provided for each column of the plurality of unit discharge regions; and phosphors of two kinds or more formed on the main surface of the second substrate covering the third electrode, having different luminescent colors, and in the plasma display panel of the fifth aspect, the first electrode has a trunk portion extending in a first direction which is a direction of the row; and branch portions connected to the trunk portion, being provided for the plurality of unit discharge regions, respectively, and protruding in a second direction which is a direction of the column, the second electrode has a trunk portion extending in the first direction; and branch portions connected to the trunk portion of the second electrode, being provided for the plurality of unit discharge regions, respectively, and protruding in the second direction to define discharge gaps between the branch portions of the first and second electrodes, respectively, and the spacings of the discharge gaps in the second direction vary among the plurality of unit discharge regions, depending on the luminescent colors.
According to a twelfth aspect of the present invention, in the plasma display panel of any one of the first to eleventh aspects further comprises a dielectric layer formed on the main surface of the first substrate covering the first electrode and the second electrode, and in the plasma display panel of the sixth aspect, the phosphors are also formed on a surface of the dielectric layer in portions which do not overlap neither the branch portions of the first electrode nor the branch portions of the second electrode in plan view.
The present invention is also directed to a plasma display device. According to a thirteenth aspect of the present invention, the plasma display device comprises: the plasma display panel of any one of the first to twelfth aspects; and a driving circuit for driving the plasma display panel.
In the plasma display panel of the first aspect of the present invention, by varying the areas of the branch portions of the first electrode, the amounts of ultraviolet rays to be irradiated on the phosphors can be varied depending on colors. Therefore, by increasing the area of the branch portion of the first electrode as the luminescence intensity in the unit discharge region becomes smaller in irradiation of the same amount of ultraviolet rays, it is possible to uniformize the luminescence intensities among the unit discharge regions for all the colors.
In the plasma display panel of the second aspect of the present invention, by varying the widths of the branch portions in the first direction, the area of branch portions of the first electrode can be varied depending on colors.
In the plasma display panel of the third aspect of the present invention, by varying the lengths of the branch portions in the second direction, the area of branch portions of the first electrode can be varied depending on colors. Moreover, it is possible to ensure sufficient allowance of misalignment in bonding the first substrate and the second substrate for all the luminescent colors.
In the plasma display panel of the fourth aspect of the present invention, decrease in the luminescence intensity of the plasma display panel caused by the branch portions of the first electrode can be minimized.
In the plasma display panel of the fifth aspect of the present invention, by varying the spacings of the discharge gaps in the second direction, the incidence of the sustain discharges can be varied depending on colors. Therefore, by setting so that the spacing of the discharge gap in the second direction may become narrower as the firing voltage of the writing discharge in the unit discharge region becomes higher, it is possible to uniformize the incidence of the sustain discharges among the unit discharge regions for all the colors.
In the plasma display panel of the sixth aspect of the present invention, after forming the first or second electrode having the branch portions whose areas are not varied thereamong and aligning with the first or second electrode, the second or first electrode having the branch portions whose areas are varied thereamong can be formed. Therefore, the first and second electrodes can be manufactured with relatively high precision.
In the plasma display panel of the seventh aspect of the present invention, as compared with the first electrode having the trunk portion and the branch portions individually formed of the different materials, it is relatively easy to manufacture the first electrode.
In the plasma display panel of the eighth aspect of the present invention, even when the branch portions of the first electrode are formed of a material having low transmissivity, decrease in the luminescence intensity of the plasma display panel can be controlled.
In the plasma display panel of the ninth aspect of the present invention, it is not required to form the trunk portion of the first electrode by aligning the trunk portion with predetermined portions on the branch portions of the first electrode. Therefore, manufacture process can be simplified.
In the plasma display panel of the tenth aspect of the present invention, the trunk portion of the first electrode is not formed in portions inside the rims of the branch portions of the first electrode. Therefore, decrease in the luminescence intensity of the plasma display panel can be further controlled.
In the plasma display panel of the eleventh aspect of the present invention, by varying the spacings of the discharge gaps in the second direction, the incidence of the sustain discharges can be varied depending on colors. Therefore, by setting the spacing of the discharge gap in the second direction as to become narrower as the firing voltage of the writing discharge in the unit discharge region becomes higher, it is possible to uniformize the incidence of the sustain discharges among the unit discharge regions for all the colors.
In the plasma display panel of the twelfth aspect of the present invention, since the phosphors are formed not only on the side of the second substrate but also on the side of the first substrate serving as a display surface, it is possible to enhance the luminance of the plasma display panel.
In the plasma display device of the thirteenth aspect of the present invention, it is possible to provide a plasma display device having excellent display characteristics.
An object of the present invention is to provide a plasma display panel capable of setting the color temperature of white to a proper value without control of the input gains which causes deterioration in the number of tones, not accompanied by wrong discharge, and a plasma display device comprising the plasma display panel.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.